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The assignment here is to make a four-function calculator. The user is supposed to type in an operator and a number, and the calculator goes to work. For example:
Enter operator and value: + 10
Total: 10
But things don't go as expected.
1 /************************************************
2 * calc -- Simple 4 function calculator. *
3 * *
4 * Usage: *
5 * $ calc *
6 * Enter operator and value: + 5 *
7 * *
8 * At the end of each operation the accumulated *
9 * results are printed. *
10 ************************************************/
11 #include <stdio.h>
12 int main() {
13 char oper; /* Operator for our calculator */
14 int result;/* Current result */
15 int value; /* Value for the operation */
16
17 result = 0;
18 while (1)
19 {
20 char line[100]; // Line from the user
21 printf("Enter operator and value:");
22
23 fgets(line, sizeof(line), stdin);
24 sscanf(line, "%c %d", oper, value);
25
26 switch (oper) {
27 case '+':
28 result += value; break;
29 case '-':
30 result -= value; break;
31 case '*':
32 result *= value; break;
33 case '/':
34 if (value == 0)
35 printf("Divide by 0 error\n");
36 else
37 result /= value;
38 break;
39 case 'q':
40 exit (0);
41 default:
42 printf("Bad operator entered\n"); break;
43 }
44 printf("Total: %d\n", result);
45 }
46 }
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One company had a problem. Some of its customers were deleting the company name and copyright from its software. The programmers were asked to come up with a way to prevent this. So they put in some code to checksum the copyright, and if it came out wrong, they would issue an error message:
Fatal error:
Water buffalos need immediate feeding
Call 1-800-555-1234 for technical support.
The idea was that this error message would be so strange that the miscreant would call technical support to find out what it meant. (What it really meant was, "I modified your program illegally.")
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